Three-dimensional field effect device

ABSTRACT

A method of forming stacked fin field effect devices is provided. The method includes forming a layer stack on a substrate, wherein the layer stack includes a first semiconductor layer on a surface of the substrate, a second semiconductor layer on the first semiconductor layer, a third semiconductor layer on the second semiconductor layer, a separation layer on the third semiconductor layer, a fourth semiconductor layer on the separation layer, a fifth semiconductor layer on the fourth semiconductor layer, and a sixth semiconductor layer on the fifth semiconductor layer. The method further includes forming a plurality of channels through the layer stack to the surface of the substrate, and removing portions of the second semiconductor layer and fifth semiconductor layer to form lateral grooves.

BACKGROUND Technical Field

The present invention generally relates to field effect transistors, andmore particularly to forming an arrangement of two or more field effecttransistors.

Description of the Related Art

A Field Effect Transistor (FET) typically has a source, a channel, and adrain, where current flows from the source to the drain, and a gate thatcontrols the flow of current through the device channel. Field EffectTransistors (FETs) can have a variety of different structures, forexample, FETs have been fabricated with the source, channel, and drainformed in the substrate material itself, where the current flowshorizontally (i.e., in the plane of the substrate), and FinFETs havebeen formed with the channel extending outward from the substrate, butwhere the current also flows horizontally from a source to a drain. Thechannel for the FinFET can be an upright slab of thin rectangularsilicon (Si), commonly referred to as the fin with a gate on the fin, ascompared to a MOSFET with a single gate parallel with the plane of thesubstrate. Depending on the doping of the source and drain, an n-FET ora p-FET can be formed.

Examples of FETs can include a metal-oxide-semiconductor field effecttransistor (MOSFET) and an insulated-gate field-effect transistor(IGFET). Two FETs also can be coupled to form a complementary metaloxide semiconductor (CMOS) device, where a p-channel MOSFET andn-channel MOSFET are coupled together.

SUMMARY

In accordance with an embodiment of the present invention, a method offorming stacked fin field effect devices is provided. The methodincludes forming a layer stack on a substrate, wherein the layer stackincludes a first semiconductor layer on a surface of the substrate, asecond semiconductor layer on the first semiconductor layer, a thirdsemiconductor layer on the second semiconductor layer, a separationlayer on the third semiconductor layer, a fourth semiconductor layer onthe separation layer, a fifth semiconductor layer on the fourthsemiconductor layer, and a sixth semiconductor layer on the fifthsemiconductor layer. The method further includes forming a plurality ofchannels through the layer stack to the surface of the substrate, andremoving portions of the second semiconductor layer and fifthsemiconductor layer to form lateral grooves.

In accordance with another embodiment of the present invention, a methodof forming stacked fin field effect devices is provided. The methodincludes forming one or more channels through a first semiconductorlayer, a second semiconductor layer, a third semiconductor layer, aseparation layer, a fourth semiconductor layer, a fifth semiconductorlayer, and a sixth semiconductor layer to a top surface of a substrate.The method further includes removing portions of the secondsemiconductor layer and fifth semiconductor layer to form lateralgrooves, and forming a gate structure in each of the lateral grooves.

In accordance with yet another embodiment of the present invention, astacked field effect device is provided. The stacked field effect deviceincludes a lower vertical transport field effect transistor segment, anupper vertical transport field effect transistor co-linear with thelower vertical transport field effect transistor, and an insulatinglayer between the upper vertical transport field effect transistorsegment and the lower vertical transport field effect transistorsegment.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a three-dimensional view showing a patterned mask layer on asemiconductor layer stack, in accordance with an embodiment of thepresent invention;

FIG. 2 is a cross-sectional side view showing a plurality of channelsformed in the semiconductor layer stack, and selective removal of aportion of some of the semiconductor layers to form lateral grooves, inaccordance with an embodiment of the present invention;

FIG. 3 is a cross-sectional side view showing formation of gatestructures in each of the lateral grooves formed in the semiconductorlayers, in accordance with an embodiment of the present invention;

FIG. 4 is a cross-sectional side view showing selective removal ofportions of other layers of the semiconductor layer stack adjacent tothe gate structures, in accordance with an embodiment of the presentinvention;

FIG. 5 is a cross-sectional side view showing a dielectric fill formedin the recessed semiconductor layers adjacent to the gate structures, inaccordance with an embodiment of the present invention;

FIG. 6 is a cross-sectional side view showing the channels filled with alithographic mask plug, in accordance with an embodiment of the presentinvention;

FIG. 7 is a cross-sectional side view showing an access trench formed inthe first and second lithographic mask layers and semiconductor stacklayers, in accordance with an embodiment of the present invention;

FIG. 8 is a cross-sectional side view showing removal of exposedportions of some of the semiconductor layers, and formation of spacerson the second and fifth semiconductor layers using selective growth, inaccordance with an embodiment of the present invention;

FIG. 9 is a cross-sectional side view showing contact slabs formed onthe spacers, in accordance with an embodiment of the present invention;

FIG. 10 is a cross-sectional side view showing portions of the secondsemiconductor layer and fifth semiconductor layer replaced with adielectric fill, in accordance with an embodiment of the presentinvention;

FIG. 11 is a cross-sectional side view showing the access trench filledwith a dielectric column, in accordance with an embodiment of thepresent invention;

FIG. 12 is a cross-sectional side view showing a stacked arrangement ofcollinear vertical transport field effect devices, in accordance with anembodiment of the present invention;

FIG. 13 is a top view showing an array of access trenches filled withdielectric columns adjacent to contact slabs and sixth semiconductorlayer sections, in accordance with an embodiment of the presentinvention;

FIG. 14 is a schematic diagram showing a stacked device circuit, inaccordance with an embodiment of the present invention; and

FIG. 15 is a three dimensional cut-away view showing conductive linesand source/drain contacts adjoining portions of stacked upper and lowervertical pillars, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

Embodiments of the present invention relate generally to formingmultiple vertical transport field effect transistors (VT FETs) stackedon top of each other to increase device density, while making thefabrication process more efficient by reducing the number of masking andetching processes involved in forming multiple devices.

Embodiments of the present invention relate generally to formingthree-dimensional (3-D) field effect devices through forming multipleco-linear vertical pillars with source/drains, and forming conductivelines orthogonal to the vertical pillars as a unified process to producemultiple vertical transport field effect transistors. The conductivelines can be formed in electrical connection with the source/drains oras part of an electrode of a gate structure by removing bars of the samematerial layer adjoining the vertical pillars. The vertical pillars canbe semiconductor material, whereas the conductive lines can be a metalor metal alloy. The device channels and top and bottom source/drains canbe formed from the adjoining layers of a stack of semiconductor layers.

Embodiments of the present invention relate generally to forming n-typeFETs and p-type FETs stacked on top of each other by alternating n-dopedand p-doped layers in a semiconductor layer stack for forming multipleVT FETs. Different regions of a substrate can have different orders ofalternating n-doped and p-doped layers, such that a different sequenceof n-type and p-type VT FETs can be formed on different regions of thesubstrate. The stacked n-type and p-type VT FETs can form CMOS devices.

Embodiments of the present invention relate generally to formingsource/drains above and/or below device channels by alternating theepitaxial growth and dopant type and dopant concentration when formingthe semiconductor layers for the vertical pillars of the multiple VTFETs. Conductive lines can be formed to the different doped layers toform the VT FET source and drain connections and the gate electrodes,where the conductive lines can span multiple source/drains or gatestructures.

Exemplary applications/uses to which the present invention can beapplied include, but are not limited to: complementarymetal-oxide-semiconductor (CMOS) devices for logic circuits (e.g., NANDgates, NOR gates, etc.) and memories (e.g., flip-flops, static randomaccess memory (SRAM), dynamic random access memory (DRAM), electricallyerasable programmable read-only memory (EEPROM), etc.), and applicationspecific integrated circuits (ASICs).

It is to be understood that aspects of the present invention will bedescribed in terms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps can be varied within the scope of aspects of the presentinvention.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a patterned mask layer on asemiconductor layer stack is shown, in accordance with an embodiment ofthe present invention.

In one or more embodiments, a substrate 110 can be, for example, asingle crystal semiconductor material wafer or asemiconductor-on-insulator stacked wafer. The substrate 110 can includea support layer that provides structural support, and an activesemiconductor layer that can form devices. An insulating layer (e.g., aburied oxide (BOX) layer) may be between the active semiconductor layerand the support layer to form a semiconductor-on-insulator substrate(SeOI) (e.g., a silicon-on-insulator substrate (SOI)), or an implantedlayer can form a buried insulating material.

The support layer can include crystalline, semi-crystalline,micro-crystalline, nano-crystalline, and/or amorphous phases. Thesupport layer can be a semiconductor (e.g., silicon (Si), siliconcarbide (SiC), silicon-germanium (SiGe), germanium (Ge),gallium-arsenide (GaAs), cadmium-telluride (CdTe), etc.), an insulator(e.g.: glass (e.g. silica, borosilicate glass), ceramic (e.g., aluminumoxide (Al₂O₃, sapphire), plastic (e.g., polycarbonate,polyacetonitrile), metal (e.g. aluminum, gold, titanium,molybdenum-copper (MoCu) composites, etc.), or combination thereof.

The wafer or active semiconductor layer can include a crystalline,semi-crystalline, micro-crystalline, nano-crystalline, and/or amorphoussemiconductor, for example, a IV or IV-IV semiconductor (e.g., silicon(Si), silicon carbide (SiC), silicon-germanium (SiGe), germanium (Ge)),a III-V semiconductor (e.g., gallium-arsenide (GaAs), indium-phosphide(InP), indium-antimonide (InSb)), a II-VI semiconductor (e.g.,cadmium-telluride (CdTe), zinc-telluride (ZnTe), zinc sulfide (ZnS),zinc selenide (ZnSe)), or a IV-VI semiconductor (e.g., tin sulfide(SnS), lead selenide (PbSb)).

The surface of the substrate 110 can have a crystalline face on whichadditional layers can be epitaxially grown/deposited, for example, asilicon {100} crystal face.

In one or more embodiments, a first semiconductor layer 120 can beformed on the surface of the substrate 110, where the firstsemiconductor layer 120 can be formed by epitaxial or heteroepitaxialgrowth on the exposed surface of the substrate 110. Epitaxy andheteroepitaxy can be done by ultrahigh vacuum chemical vapor deposition(UHVCVD), rapid thermal chemical vapor deposition (RTCVD), metalorganicchemical vapor deposition (MOCVD), low-pressure chemical vapordeposition (LPCVD), limited reaction processing CVD (LRPCVD), molecularbeam epitaxy (MBE). Epitaxial materials may be grown from gaseous orliquid precursors. Epitaxial materials may be grown using vapor-phaseepitaxy (VPE), molecular-beam epitaxy (MBE), liquid-phase epitaxy (LPE),or other suitable process. Epitaxial silicon, silicon germanium (SiGe),carbon doped silicon (Si:C) and/or silicon carbide (SiC) can be dopedduring deposition (in-situ doped) by adding dopants, n-type dopants(e.g., phosphorus or arsenic) or p-type dopants (e.g., boron orgallium), depending on the type of device being fabricated (e.g., n-typeor p-type). The terms “epitaxial growth and/or deposition” and“epitaxially formed and/or grown,” relates to the growth of acrystalline material on a deposition surface of another crystallinematerial, in which the material being formed (also referred to as acrystalline over layer) has substantially the same crystallinecharacteristics as the material of the deposition surface (e.g., seedmaterial). Heteroepitaxy refers to epitaxial growth of a material with adifferent chemical composition than the seed material on the depositionsurface.

In various embodiments, the in-situ doping can be controlled to formlayers alternating between n-type dopants, no dopants (i.e., intrinsic),and p-type dopants, to form top and bottom source/drains with anintrinsic semiconductor device channel layer in between the source/drainlayers. At least six semiconductor layers can beepitaxially/heteroepitaxially grown on each other to form thesemiconductor layer stack. The sequence of doped and undoped layers witha separation layer in between can be repeated to form additional devisesstacked on top of one another.

In one or more embodiments, the first semiconductor layer 120 can be asemiconductor material, including, but not limited to, silicon (Si),silicon-germanium (SiGe), carbon-doped silicon (Si:C), silicon carbide(SiC), gallium nitride (GaN), gallium arsenide (GaAs), molybdenumsulfide (MoS), or a combination thereof.

In various embodiments, the first semiconductor layer 120 can be n-dopedor p-doped to form a bottom source/drain.

In one or more embodiments, the first semiconductor layer 120 can have athickness in a range of about 10 nanometers (nm) to about 20 nm, or in arange of about 12 nm to about 15 nm, although other thicknesses are alsocontemplated. The thickness of the first semiconductor layer 120 candetermine the thickness (length) of a subsequently formed bottomsource/drain for a lower VT FET.

In one or more embodiments, a second semiconductor layer 130 can beformed on the surface of the first semiconductor layer 120, wherein thesecond semiconductor layer 130 can be formed by epitaxial orheteroepitaxial growth (e.g., MBE, VPE, LPCVD, etc.).

In various embodiments, the second semiconductor layer 130 may not bedoped. The second semiconductor layer 130 can provide an intrinsicsemiconductor layer between subsequently formed doped semiconductorlayers to form a lower VT FET device channel.

In one or more embodiments, the second semiconductor layer 130 can havea thickness in a range of about 10 nm to about 30 nm, or in a range ofabout 15 nm to about 25 nm, although other thicknesses are alsocontemplated. The thickness of the second semiconductor layer 130 candetermine the length of a subsequently formed device channel for a lowerVT FET.

In one or more embodiments, the second semiconductor layer 130 can becan be a semiconductor material, including, but not limited to, silicon(Si), silicon-germanium (SiGe), carbon-doped silicon (Si:C), siliconcarbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs),molybdenum sulfide (MoS), or a combination thereof. The secondsemiconductor layer 130 can be a different semiconductor material thanthe first semiconductor layer 120, where the second semiconductor layer130 can have a different chemical composition/different chemicalconcentrations than the first semiconductor layer 120.

In one or more embodiments, a third semiconductor layer 140 can beformed on the surface of the second semiconductor layer 130, wherein thethird semiconductor layer 140 can be formed by epitaxial orheteroepitaxial growth (e.g., MBE, VPE, LPCVD, etc.). The firstsemiconductor layer 120, second semiconductor layer 130, and thirdsemiconductor layer 140 can have the same crystal structure andorientation as the substrate 110 through the epitaxial/heteroepitaxialgrowth process.

In one or more embodiments, the third semiconductor layer 140 can be asemiconductor material, including, but not limited to, silicon (Si),silicon-germanium (SiGe), carbon-doped silicon (Si:C), or siliconcarbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs),molybdenum sulfide (MoS), or a combination thereof. The thirdsemiconductor layer 140 can be a different semiconductor material thanthe second semiconductor layer 130, where the third semiconductor layer140 can have a different chemical composition/different chemicalconcentrations than the second semiconductor layer 130. The firstsemiconductor layer 120 and third semiconductor layer 140 may be thesame semiconductor material, and may have the same doping type (n-typeor p-type). In various embodiments, the third semiconductor layer 140can be n-doped or p-doped to form a top source/drain.

In one or more embodiments, the third semiconductor layer 140 can have athickness in a range of about 10 nm to about 20 nm, or in a range ofabout 12 nm to about 15 nm, although other thicknesses are alsocontemplated. The thickness of the third semiconductor layer 140 candetermine the thickness (length) of a subsequently formed topsource/drain for a lower VT FET.

In one or more embodiments, a separation layer 150 can be formed on thesurface of the third semiconductor layer 140, wherein the separationlayer 150 can be formed by expitaxy or heteroepitaxy. The use ofexpitaxy and/or heteroepitaxy can maintain the crystallinity and crystalorientation of each of the semiconductor layers formed for the stack.

In one or more embodiments, the separation layer 150 can have athickness in a range of about 20 nm to about 50 nm, or in a range ofabout 30 nm to about 40 nm, although other thicknesses are alsocontemplated. The separation layer 150 can provide a sacrificial layerfor later replacement by an insulating layer between vertically adjacentsource/drains and gates of a VT FET.

In one or more embodiments, the separation layer 150 can be asemiconductor material, including, but not limited to, silicon (Si),silicon-germanium (SiGe), silicon carbide (SiC), gallium nitride (GaN),gallium arsenide (GaAs), molybdenum sulfide (MoS), or a combinationthereof. The separation layer 150 can be a different material from thethird semiconductor layer 140, the second semiconductor layer 130,and/or the first semiconductor layer 120 to allow selective removal.

In one or more embodiments, a fourth semiconductor layer 160 can beformed on the surface of the separation layer 150, where the fourthsemiconductor layer 160 can be formed by epitaxy or heteroepitaxy.

In one or more embodiments, the fourth semiconductor layer 160 can havea thickness in a range of about 10 nm to about 20 nm, or in a range ofabout 12 nm to about 15 nm, although other thicknesses are alsocontemplated. The thickness of the fourth semiconductor layer 160 candetermine the thickness of a subsequently formed bottom source/drain foran upper VT FET.

In one or more embodiments, the fourth semiconductor layer 160 can be asemiconductor material, including, but not limited to, silicon (Si),silicon-germanium (SiGe), carbon-doped silicon (Si:C), or siliconcarbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs),molybdenum sulfide (MoS), or a combination thereof.

In various embodiments, the fourth semiconductor layer 160 can be dopedwith a dopant of the opposite type from the first semiconductor layer120 and third semiconductor layer 130 (i.e., an n-type dopant instead ofa p-type dopant, or vice versa).

In one or more embodiments, a fifth semiconductor layer 170 can beformed on the fourth semiconductor layer 160, where the fifthsemiconductor layer 170 can be formed by epitaxy or heteroepitaxy.

In one or more embodiments, the fifth semiconductor layer 170 can be asemiconductor material, including, but not limited to, silicon (Si),silicon-germanium (SiGe), carbon-doped silicon (Si:C), or siliconcarbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs),molybdenum sulfide (MoS), or a combination thereof. The fifthsemiconductor layer 170 can be a different semiconductor material thanthe fourth semiconductor layer 160, where the fifth semiconductor layer170 can have a different chemical composition/different chemicalconcentrations than the fourth semiconductor layer 160.

In various embodiments, the fifth semiconductor layer 170 may not bedoped. The fifth semiconductor layer 170 can provide an intrinsicsemiconductor layer between doped semiconductor layers to form an upperVT FET device channel.

In one or more embodiments, the fifth semiconductor layer 170 can have athickness in a range of about 10 nm to about 30 nm, or in a range ofabout 15 nm to about 25 nm, although other thicknesses are alsocontemplated. The thickness of the fifth semiconductor layer 170 candetermine the length of a subsequently formed device channel for anupper VT FET.

In one or more embodiments, a sixth semiconductor layer 180 can beformed on the surface of the fifth semiconductor layer 170, where thesixth semiconductor layer 180 can be formed by epitaxy or heteroepitaxy.

In one or more embodiments, the sixth semiconductor layer 180 can be asemiconductor material, including, but not limited to, silicon (Si),silicon-germanium (SiGe), carbon-doped silicon (Si:C), or siliconcarbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs),molybdenum sulfide (MoS), or a combination thereof. The sixthsemiconductor layer 180 can be a different semiconductor material thanthe fifth semiconductor layer 170, where the sixth semiconductor layer180 can have a different chemical composition/different chemicalconcentrations than the fifth semiconductor layer 170. The sixthsemiconductor layer 180 and fourth semiconductor layer 160 may be thesame semiconductor material, and may have the same doping type (n-typeor p-type). In various embodiments, the sixth semiconductor layer 180can be n-doped or p-doped to form a top source/drain.

In one or more embodiments, the sixth semiconductor layer 180 can have athickness in a range of about 10 nm to about 20 nm, or in a range ofabout 12 nm to about 15 nm, although other thicknesses are alsocontemplated. In various embodiments, the sixth semiconductor layer 180can be n-doped or p-doped to form a top source/drain for an upper VT FETdevice.

In one or more embodiments, additional sequences of the separation layerand semiconductor layers can be formed on top of the sixth semiconductorlayer 180 to provide a suitable layer stack for forming a predeterminednumber of additional stacked VT FET devices. The separation layer can beformed between each pair of adjacent doped semiconductor layers toseparate the stacked devices.

In various embodiments, the semiconductor layers can besilicon-germanium with different concentrations of germanium to controlthe etch rates of each layer, so different semiconductor layers can beselectively removed. Selective removal refers to the ability to removeone material without notably effecting other materials due todifferences in etch rate and/or etch chemistry. In various embodiments,the semiconductor layers 130, 170 intended to form device channels inthe vertical pillars can have a greater germanium concentration than thesemiconductor layers 120, 140, 160, 180 intended to form top and bottomsource/drains, where the germanium concentration of semiconductor layers130, 170 can be from about 10 atomic percent (at. %) to about 90 at. %,or about 20 at. % to about 90 at. %, or about 50 at. % to about 90 at.%, or about 20 at. % to about 80 at. %, or about 60 at. % to about 80at. %, although other concentrations are also contemplated. Thegermanium concentration of the semiconductor layers 120, 140, 160, 180can be from about 1 atomic percent (at. %) to about 80 at. %, or about 2at. % to about 60 at. %, or about 10 at. % to about 50 at. %, or about 5at. % to about 40 at. %, or about 10 at. % to about 30 at. %, althoughother concentrations are also contemplated, where the germaniumconcentration of the semiconductor layers 120, 140, 160, 180 is lowerthan the germanium concentration of the semiconductor layers 130, 170.In various embodiments, the semiconductor layers 130, 170 can be 100 at.% germanium.

In a non-limiting exemplary embodiment, semiconductor layers 120, 140,160, 180 can have a germanium concentration of about 25 at. % andsemiconductor layers 130, 170 can have a germanium concentration ofabout 55 at. %.

In various embodiments, semiconductor layers intended to form n-typesource/drains can be silicon (Si), carbon-doped silicon (Si:C) orsilicon carbide (SiC), and the semiconductor layers intended to formp-type source/drains can be silicon (Si) or silicon-germanium (SiGe).

In one or more embodiments, a lithographic mask layer 190 can be formedon the sixth semiconductor layer 180, where the lithographic mask layer190 can be blanket deposited, for example, by chemical vapor deposition(CVD), plasma enhance CVD (PECVD), or spin-on. The lithographic masklayer 190 can be a hardmask, a softmask, or a combination thereof. Ahardmask can be a dielectric material. A soft mask can be a polymericresist material that can be patterned and developed through alithographic process, and the pattern transferred to underlying layersincluding the hardmask.

In one or more embodiments, the lithographic mask layer 190 can bepatterned and developed to form a plurality of openings 195 that exposesportions of the sixth semiconductor layer 180, where the pattern ofopenings 195 can be transferred to the underlying layers by etching toform channels. The openings 195 can form a row×column array. The size ofthe openings can determine the lateral (i.e., parallel to the plane ofthe substrate) length of subsequently formed device features.

FIG. 2 is a cross-sectional side view showing a plurality of channelsformed in the semiconductor layer stack, and selective removal of aportion of some of the semiconductor layers, in accordance with anembodiment of the present invention.

In one or more embodiments, portions of the sixth semiconductor layer180 exposed by openings 195 in lithographic mask layer 190 and portionsof the underlying layers 170, 160, 150, 140, 130, 120 can be removedusing a non-selective, directional etch, or a sequence of selectivedirectional etches (e.g., reactive ion etch (RIE)) for each of thematerials of the underlying layers to form channels 200 through thesemiconductor layers down to the surface of the substrate 110.

In one or more embodiments, channels 200 can have a width in a range ofabout 10 nm to about 30 nm, or about 15 nm to about 25 nm, althoughother widths are contemplated.

In one or more embodiments, channels 200 can have a length in a range ofabout 10 nm to about 100 nm, or about 40 nm to about 75 nm, althoughother lengths are contemplated. The length of the channels 200 candetermine the length of grooves and recesses formed in the underlyinglayers that can be used to form gate structures and source/draincontacts.

The Height/Width aspect ratio of channels can be about 4.5 or up to 4.5,which depends on the stacked vertical device number and selectiveprocess margin.

In one or more embodiments, the separation layer 150 can be removed andreplaced with an insulating layer 155, where the insulating layer 155can be formed, for example, by ALD, PEALD, CVD, PECVD, or a combinationthereof. Portions of the semiconductor layer stack around the peripheryof each channel 200 can support the semiconductor layers 160, 170, 180,and lithographic mask layer 190 while the portion of the separationlayer 150 is removed and replaced with insulating layer 155. The processcan be repeated until the exposed portion of the separation layer 150 isreplaced and the channels 200 are reopened down to the substratesurface.

In one or more embodiments, a portion of the second semiconductor layer130 and a portion of the fifth semiconductor layer 170 can be the samematerial, which can have essentially the same elemental composition(e.g., Si_(x)Ge_(1-x)), so portions of the semiconductor layers 130, 170can be removed at the same time. A portions of the second semiconductorlayer 130 and a portion of the fifth semiconductor layer 170 can beremoved using a selective isotropic etch, (e.g., wet chemical etch, dryplasma etch) to form lateral grooves 205 in the second semiconductorlayer 130 and fifth semiconductor layer 170. The grooves 205 can extendalong the length of the channel 200, and may extend beyond the ends ofthe channels 200.

In one or more embodiments, the lateral grooves 205 can be formed to adepth of about 10 nm to about 30 nm into the second semiconductor layer130 and fifth semiconductor layer 170.

FIG. 3 is a cross-sectional side view showing formation of gatestructures in each of the lateral grooves formed in the semiconductorlayers, in accordance with an embodiment of the present invention.

In one or more embodiments, a gate structure can be formed in each ofthe lateral grooves 205. A gate structure can include a gate dielectriclayer 210, a work function layer 220, and a gate fill layer 230.

In one or more embodiments, a gate dielectric layer 210 can be formed onthe exposed portions of the second semiconductor layer 130 and fifthsemiconductor layer 170, and exposed surfaces of the adjacent firstsemiconductor layer 120 and third semiconductor layer 140, or theadjacent fourth semiconductor layer 160 and sixth semiconductor layer180, and a work function layer 220 can be formed on the gate dielectriclayer, where the gate dielectric layer 210 and work function layer 220can be formed by conformal depositions (e.g., atomic layer deposition(ALD) or plasma enhanced ALD (PEALD)).

In one or more embodiments, a gate dielectric layer 210 can be siliconoxide (SiO), silicon nitride (SiN), silicon oxynitride (SiON), boronnitride (BN), high-k dielectric materials, or a combination thereof.Examples of high-k materials include but are not limited to metaloxides, such as, hafnium oxide (HfO), hafnium silicon oxide (HfSiO),hafnium silicon oxynitride (HfSiON), lanthanum oxide (LaO), lanthanumaluminum oxide (LaAlO), zirconium oxide (ZrO), zirconium silicon oxide(ZrSiO), zirconium silicon oxynitride (ZrSiON), tantalum oxide (TaO),titanium oxide (TiO), barium strontium titanium oxide (BaSrTiO), bariumtitanium oxide (BaTiO), strontium titanium oxide (SrTiO), yttrium oxide(YO), aluminum oxide (AlO), lead scandium tantalum oxide (PbScTaO), andlead zinc niobate (PbZnNbO). The high-k material may further includedopants such as lanthanum, aluminum, magnesium, or combinations thereof.

In various embodiments, the gate dielectric layer 210 can have athickness in the range of about 7 Å to about 30 Å, or about 7 Å to about10 Å, or about 1 nm to about 2 nm, although other thicknesses arecontemplated.

In various embodiments, the work function layer 220 can include, but notnecessarily be limited to, titanium nitride (TiN), tantalum nitride(TaN) or ruthenium (Ru), for a PFET. The work function layer 220 caninclude, but not necessarily be limited to, titanium nitride (TiN),titanium aluminum nitride (TiAlN), titanium aluminum carbon nitride(TiAlCN), titanium aluminum carbide (TiAlC), tantalum aluminum carbide(TaAlC), tantalum aluminum carbon nitride (TaAlCN), lanthanum (La) dopedTiN or lanthanum (La) doped TaN, for an NFET. The work function material(WFM) can form the work function layer 220 on the gate dielectric layer210.

The work function layer 220 can have a thickness in the range of about 1nm to about 10 nm, or about 2 nm to about 5 nm, or about 1 nm to about 3nm, or about 2 nm, although other thicknesses are contemplated.

In one or more embodiments, a gate fill layer 230 can be formed on thegate dielectric layer 210 and work function layer 220, where the gatefill layer 230 can be formed by a conformal deposition (e.g., ALD).

In various embodiments, the gate fill layer 230 can be made of aconductive material, which can be a metal, for example, tungsten (W),copper (Cu), cobalt (Co), tantalum (Ta), titanium (Ti), manganese (Mn);a conductive metal compound, for example, tantalum nitride (TaN),titanium nitride (TiN), titanium carbide (TiC), a copper manganese alloy(Cu—Mn), or any suitable combination thereof.

An etch back can be used to remove deposited gate fill layer 230, workfunction layer 220, and/or gate dielectric layer 210 materials from thechannel 200. Excess gate dielectric layer 210 material, work functionlayer 220 material, and gate fill layer 230 material deposited on thesidewalls of the channel 200 formed by the other surfaces can be removedusing an isotropic etch and/or RIE.

FIG. 4 is a cross-sectional side view showing selective removal ofportions of other layers of the semiconductor layer stack adjacent tothe gate structures, in accordance with an embodiment of the presentinvention.

In one or more embodiments, portions of the first semiconductor layer120, third semiconductor layer 140, fourth semiconductor layer 160, andsixth semiconductor layer 180 can be removed using a selective isotropicetch, (e.g., wet chemical etch, dry plasma etch) to form lateral grooves206 adjacent to the gate dielectric layers 210 of each of the gatestructures. The first semiconductor layer 120 and third semiconductorlayer 140 can be the same material so the portions can be removedsimultaneously with the same etch. The fourth semiconductor layer 160and sixth semiconductor layer 180 can be the same material, so theportions can be removed simultaneously with the same etch. The first,third, fourth, and sixth layers can all be the same material.

In various embodiments, the lateral grooves 206 can be about the samedepth into the semiconductor layers as the lateral grooves 205 formed insecond semiconductor layer 130 and fifth semiconductor layer 170, so theend face of the first semiconductor layer 120, third semiconductor layer140, fourth semiconductor layer 160, and sixth semiconductor layer 180can be co-planar with the interface between the gate dielectric layer210 and the second semiconductor layer 130 and the fifth semiconductorlayer 170.

FIG. 5 is a cross-sectional side view showing a dielectric fill formedin the recessed semiconductor layers adjacent to the gate structures, inaccordance with an embodiment of the present invention.

In one or more embodiments, a dielectric fill 157 can be formed in thelateral grooves 206 adjacent to the gate structures, where thedielectric fill can be the same material as insulating layer 155. Thedielectric fills 157 can be an insulating, dielectric material,including, but not limited to, silicon oxide (SiO), silicon nitride(SiN), a silicon oxynitride (SiON), a silicon carbonitride (SiCN), asilicon boronitride (SiBN), a silicon borocarbide (SiBC), a low-Kdielectric, or combinations thereof.

In various embodiments, the dielectric fill 157 can be formed using aconformal deposition (e.g., ALD, PEALD) and material formed on the gatestructures and sidewalls of channel 200 can be removed using anisotropic etch and or directional etch (e.g., RIE) to each back thedielectric material not in grooves 206.

FIG. 6 is a cross-sectional side view showing the channels filled with alithographic mask plug, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a second lithographic mask layer 240 can bedeposited on the first lithographic mask layer 190 to fill in each ofthe channels 200 with lithographic mask plugs 245. Material of thesecond lithographic mask layer 240 on the first lithographic mask layer190 can be at least partially removed using a chemical-mechanicalpolishing (CMP) to provide a smooth, flat surface for lithography andpatterning.

FIG. 7 is a cross-sectional side view showing an access trench formed inthe first and second lithographic mask layers and semiconductor stacklayers, in accordance with an embodiment of the present invention.

In one or more embodiments, one or more access trenches 250 can beformed in the second lithographic mask layer 240, first lithographicmask layer 190, sixth semiconductor layer 180, fifth semiconductor layer170, and underlying layers 160, 150, 140, 130, 120, down to the topsurface of the substrate 110. The access trenches 250 can be formed by anon-selective, directional etch, or sequential selective directionaletches.

In one or more embodiments, the one or more trenches 250 can be formed adistance from each of the gate structures on the opposite side of asegment of the second semiconductor layer 130 and fifth semiconductorlayer 170. The lateral distance, D, from the interface of the gatedielectric layer 210 with the adjoining portions of the secondsemiconductor layer 130 or fifth semiconductor layer 170 can be in therange of about 10 nm to about 100 nm, or about 20 nm to about 100 nm, orabout 20 nm to about 60 nm, or about 30 nm to about 60 nm, althoughother distances are contemplated. The access trench 250 can beequidistant from each of the gate dielectric layer/semiconductorinterfaces on the same semiconductor layer. The access trenches 250 canhave sidewalls that expose each of the layers 190, 180, 170, 160, 150,140, 130, 120 down to the substrate 110. The lateral distance, D, fromthe interface of the gate dielectric layer 210 can determine the widthof segments of the layers 180, 170, 160, 150, 140, 130, 120 formingsource/drains and device channels.

In one or more embodiments, access trenches 250 can have a width in arange of about 10 nm to about 30 nm, or about 15 nm to about 25 nm,although other widths are contemplated.

In one or more embodiments, access trenches 250 can have a length in arange of about 10 nm to about 100 nm, or about 40 nm to about 75 nm,although other lengths are contemplated.

FIG. 8 is a cross-sectional side view showing removal of exposedportions of some of the semiconductor layers, and formation of spacerson the second and fifth semiconductor layers using selective growth, inaccordance with an embodiment of the present invention.

In one or more embodiments, portions of the first semiconductor layer120, third semiconductor layer 140, fourth semiconductor layer 160, andsixth semiconductor layer 180 can be removed using a selective isotropicetch, (e.g., wet chemical etch, dry plasma etch) to form lateral grooves255 spaced apart from the gate dielectric layers 210 of each of the gatestructures. A portion of the first semiconductor layer 120, thirdsemiconductor layer 140, fourth semiconductor layer 160, and sixthsemiconductor layer 180 can remain between the lateral grooves 255 andthe gate structures to form first semiconductor layer sections 125,third semiconductor layer sections 145, fourth semiconductor layersections 165, and sixth semiconductor layer sections 185. The firstsemiconductor layer 120 and third semiconductor layer 140 can be thesame material, so the portions can be removed simultaneously with thesame etch. The fourth semiconductor layer 160 and sixth semiconductorlayer 180 can be the same material, so the portions can be removedsimultaneously with the same etch. The semiconductor layer sections 125,145, 165, 185, can be the same material.

In various embodiments, the lateral grooves 255 can have a depth in arange of about 10 nm to about 30 nm, although other depths arecontemplated. The lateral grooves 255 can have a depth less than thedistance, D, such that a semiconductor layer section 125, 145, 165, 185remains above and/or below the second semiconductor layer 130 and fifthsemiconductor layer 170.

In one or more embodiments, a spacer 260 can be formed on opposite sidesof the second semiconductor layer 130 and fifth semiconductor layer 170,where the spacer 260 can be formed by a selective oxidation of theexposed sides of the second semiconductor layer 130 and fifthsemiconductor layer 170. The spacers 260 can have a thickness in a rangeof about 1 nm to about 10 nm, or about 2 nm to about 5 nm, where thethickness can be less than or equal to a third (⅓) of the thickness ofthe second semiconductor layer 130 or fifth semiconductor layer 170.Portions of oxidized second semiconductor layer 130 and fifthsemiconductor layer 170 in the access trenches 250 can be removed usinga directional etch (e.g., RIE). The oxidation process can be selectivefor semiconductor layers 130, 170 having a higher germaniumconcentration over semiconductor layers 120, 140, 160, 180.

FIG. 9 is a cross-sectional side view showing contact slabs formed onthe spacers, in accordance with an embodiment of the present invention.

In one or more embodiments, a contact slab 270 can be formed on thespacers 260 in the remaining portion of the lateral grooves 255, wherethe contact slab 270 can be formed by a conformal deposition (e.g., ALD,PEALD) and/or MOCVD. An etch back can be used to remove materials fromthe access trench 250.

In one or more embodiments, the contact slab 270 can be made of aconductive material, which can be a metal, for example, tungsten (W),copper (Cu), cobalt (Co), tantalum (Ta), titanium (Ti), manganese (Mn);a conductive metal compound, for example, tantalum nitride (TaN),titanium nitride (TiN), titanium carbide (TiC), a copper manganese alloy(Cu—Mn), or any suitable combination thereof.

FIG. 10 is a cross-sectional side view showing portions of the secondsemiconductor layer and fifth semiconductor layer replaced with adielectric fill, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a portion of the second semiconductor layer130 and fifth semiconductor layer 170 exposed by the access trench 250can be removed using a selective etch to form a second semiconductorlayer section 135 and fifth semiconductor layer section 175.

In one or more embodiments, the first semiconductor layer sections 125,second semiconductor layer section 135, third semiconductor layersections 145, fourth semiconductor layer sections 165, fifthsemiconductor layer sections 175, and sixth semiconductor layer sections185 can have a width in a range of about 10 nm to about 100 nm minus thedepth of the lateral grooves 255 in a range of about 10 nm to about 30nm.

In various embodiments, the first semiconductor layer sections 125,second semiconductor layer section 135, third semiconductor layersections 145, fourth semiconductor layer sections 165, fifthsemiconductor layer sections 175, and sixth semiconductor layer sections185 can have a width, W, in a range of about 10 nm to about 90 nm, or ina range of about 10 nm to about 70 nm, or in a range of about 10 nm toabout 30 nm, although other widths are contemplated.

In various embodiments, a dielectric plug 158 can be formed in thespaces created by removing the portions of the second semiconductorlayer 130 and fifth semiconductor layer 170.

In one or more embodiments, the dielectric plugs 158 can be aninsulating, dielectric material, including, but not limited to, siliconoxide (SiO), silicon nitride (SiN), a silicon oxynitride (SiON), asilicon carbonitride (SiCN), a silicon boronitride (SiBN), a siliconborocarbide (SiBC), a low-K dielectric, or combinations thereof. Thedielectric plugs 158 can be the same material as insulating layer 155and dielectric fills 157.

In various embodiments, the dielectric plug 158 can be formed using aconformal deposition (e.g., ALD, PEALD).

In various embodiments, the fourth semiconductor layer sections 165,fifth semiconductor layer sections 175, and sixth semiconductor layersections 185 adjacent to an upper gate structure can form an upper VTFET segment, and the first semiconductor layer sections 125, secondsemiconductor layer section 135, third semiconductor layer sections 145adjacent to a lower gate structure can form a lower VT FET segment.

FIG. 11 is a cross-sectional side view showing the access trench filledwith a dielectric column, in accordance with an embodiment of thepresent invention.

In one or more embodiments, a dielectric column 280 can be formed in theaccess trench 250, where the dielectric column 280 can be the samematerial as insulating layer 155, dielectric plug 158, and dielectricfill 157. The dielectric column 280 can be an insulating, dielectricmaterial, including, but not limited to, silicon oxide (SiO), siliconnitride (SiN), a silicon oxynitride (SiON), a silicon carbonitride(SiCN), a silicon boronitride (SiBN), a silicon borocarbide (SiBC), alow-K dielectric, or combinations thereof. A CMP can be used to removeportions of the dielectric column 280 above the top surface of thesecond lithographic mask layer 240.

FIG. 12 is a cross-sectional side view showing a stacked arrangement ofcollinear vertical transport field effect devices, in accordance with anembodiment of the present invention.

In one or more embodiments, a plurality of access trenches 250 can beformed to allow fabrication of multiple spacers 260, contact slabs 270,and upper VT FET segments 300, including, the fourth semiconductor layersections 165, fifth semiconductor layer sections 175, and sixthsemiconductor layer sections 185 adjacent to an upper gate structure,including, gate dielectric layer 210, work function layer 220, and gatefill layer 230.

In one or more embodiments, a plurality of access trenches 250 can beformed to allow fabrication of multiple spacers 260, contact slabs 270,and lower VT FET segments 310, including, the first semiconductor layersections 125, second semiconductor layer sections 135, and thirdsemiconductor layer sections 145 adjacent to a lower gate structure,including, gate dielectric layer 210, work function layer 220, and gatefill layer 230.

The combination of an upper VT FET segment 300 and a lower VT FETsegment 310 can form a stacked arrangement of two vertical transportfield effect transistors, where the fourth semiconductor layer section165 and sixth semiconductor layer section 185 are doped to form top andbottom source/drains, and the fifth semiconductor layer section 175forms a device channel of the upper VT FET segment 300. The firstsemiconductor layer section 125 and third semiconductor layer section145 are doped to form top and bottom source/drains, and the secondsemiconductor layer section 135 forms a device channel of the lower VTFET segment 310.

The contact slabs 270 can form electrical connections to the top andbottom source/drains, and the gate fill layer 230 can electricallycouple the gate structures of adjacent upper VT FET segments 300together, and electrically couple the gate structures of adjacent lowerVT FET segments 310 together to form the stacked arrangement of twovertical transport field effect transistors. The number of stackedvertical transport field effect transistors can be increased by formingadditional semiconductor layers on the semiconductor layer stack to formadditional VT FET segments above the upper VT FET segment 300.

The access trenches 250 can each be filled with dielectric column 280that electrically isolates adjacent vertical transport field effecttransistors. The lithographic mask plugs 245 can also be removed andfilled with dielectric column 280.

FIG. 13 is a top view showing an array of access trenches filled withdielectric columns adjacent to contact slabs and sixth semiconductorlayer sections, in accordance with an embodiment of the presentinvention.

In various embodiments, the channels 200 and access trenches 250 can bearranged in an array (row×column) to form multiple stacked verticaltransport field effect transistors. The size and positioning of thechannels 200 and access trenches 250 can determine the sizes and spacingof the vertical transport field effect transistors.

In various embodiments, larger channels 200 and access trenches 250 canbe cut into smaller sizes by masking and etching isolation trenches thatintersect the channels 200 and access trenches 250. The isolationtrenches 290 can electrically separate first semiconductor layersections 125, second semiconductor layer section 135, thirdsemiconductor layer sections 145, fourth semiconductor layer sections165, fifth semiconductor layer sections 175, and sixth semiconductorlayer sections 185 into shorter semiconductor layer sections, and removeportions of the semiconductor layers 120, 130, 140, 160, 170, 180 thatwould otherwise wrap around the ends of the channels 200 and accesstrenches 250 to electrically connect the semiconductor layer sections ofadjacent upper VT FET segments 300 and lower VT FET segments 310together. The isolation trenches 290 can also cut contact slabs 270 andgate structures to form separate devices.

The isolation trenches 290 can be filled with an insulating, dielectricmaterial.

FIG. 14 is a schematic diagram showing a stacked device circuit, inaccordance with an embodiment of the present invention.

In one or more embodiments, a stacked arrangement of two or morevertical transport field effect transistors can be electrically coupledto form a CMOS circuit, an inverter circuit, a flip-flop, or anelectrically erasable programmable read-only memory (EEPROM) circuit.The upper device 450 can be electrically coupled to the lower device 460through the contact slabs 270 with conductive lines 400. The upperdevice 450 can be formed by an upper VT FET segment 300 and gatestructure, and the lower device 460 can be formed by a lower VT FETsegment 310 and gate structure. The lower contact slabs 270 can beelectrically connected to ground (GND). The upper contact slabs 270 canbe electrically connected to a drain voltage, Vdd. The fourthsemiconductor layer sections 165 can be electrically connected to thirdsemiconductor layer sections 145 to provide a signal out line (OUT). Thegate fill layer 230 of the upper device and lower device can beelectrically coupled and connected to a signal in line (IN).

FIG. 15 is a three dimensional cut-away view showing conductive linesand source/drain contacts adjoining portions of stacked upper and lowervertical fin segments, in accordance with an embodiment of the presentinvention.

In various embodiments, stacked upper and lower VT FET segments 300, 310can be in electrical contact with the source/drain slabs 270. The gatefill layers 230 can couple the gates of adjacent VT FET segmentstogether, and conductive lines can electrically connect the gate filllayers 230 to couple the gate structures of stacked devices together.

The upper device can be electrically coupled to the lower device throughthe source/drain slabs 270 with conductive lines parallel with thevertical pillars forming the upper and lower VT FET segments 300, 310.

The insulating layer 155 can electrically isolate the upper VT FETsegment 300 and gate structure from the lower VT FET segment 310 andgate structure.

The upper vertical transport field effect transistor segment 300 and thelower vertical transport field effect transistor segment 310 can eachhave a height in a range of about 30 nm to about 70 nm. The uppervertical transport field effect transistor segment and the lowervertical transport field effect transistor segment can have a width, W,in a range of about 10 nm to about 90 nm. The vertical distance betweenthe upper vertical transport field effect transistor segment and thelower vertical transport field effect transistor segment occupied by theinsulating layer 155 can be in a range of about 20 nm to about 50 nm.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment”,as well as other variations thereof, means that a particular feature,structure, characteristic, and so forth described in connection with theembodiment is included in at least one embodiment. Thus, the appearancesof the phrase “in one embodiment” or “in an embodiment”, as well anyother variations, appearing in various places throughout thespecification are not necessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein can be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or one or more intervening layers can also be present.

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

Having described preferred embodiments of a system and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

What is claimed is:
 1. A stacked device circuit, comprising: a firstsemiconductor layer section on a substrate; a dielectric fill on thesubstrate adjoining the first semiconductor layer section; a secondsemiconductor layer section on the first semiconductor layer section; alower gate structure on the dielectric fill and adjoining the secondsemiconductor layer section; a third semiconductor layer section on thesecond semiconductor layer section; and an insulating layer on the thirdsemiconductor layer section and lower gate structure.
 2. The stackeddevice circuit of claim 1, further comprising a fourth semiconductorlayer section on the insulating layer.
 3. The stacked device circuit ofclaim 2, further comprising a first contact slab in electrical contactwith the first semiconductor layer section, and a second contact slab inelectrical contact with the third semiconductor layer section.
 4. Thestacked device circuit of claim 3, further comprising a fifthsemiconductor layer section on the fourth semiconductor layer sectionand a sixth semiconductor layer section on the fifth semiconductor layersection.
 5. The stacked device circuit of claim 4, further comprising athird contact slab in electrical contact with the fourth semiconductorlayer section, and a fourth contact slab in electrical contact with thesixth semiconductor layer section.
 6. The stacked field effect device ofclaim 5, wherein the first semiconductor layer section, secondsemiconductor layer section, and the third semiconductor layer sectionhas a combined height in a range of about 30 nm to about 70 nm.
 7. Thestacked field effect device of claim 6, wherein the first semiconductorlayer section has a thickness in a range of about 10 nanometers (nm) toabout 20 nm, the second semiconductor layer section has a thickness in arange of about 10 nm to about 30 nm, and the third semiconductor layersection has a thickness in a range of about 10 nm to about 20 nm.
 8. Thestacked field effect device of claim 7, wherein the insulating layer hasa thickness between the fourth semiconductor layer section and the thirdsemiconductor layer section in a range of about 20 nm to about 50 nm. 9.The stacked field effect device of claim 8, wherein the firstsemiconductor layer section, second semiconductor layer section, andthird semiconductor layer section, are silicon-germanium (SiGe), andwherein the first semiconductor layer section and third semiconductorlayer section have a lower germanium concentration than the secondsemiconductor layer section.
 10. A stacked device circuit, comprising: afirst semiconductor layer section on a substrate; a dielectric fill onthe substrate adjoining the first semiconductor layer section; a secondsemiconductor layer section on the first semiconductor layer section; alower gate structure on the dielectric fill and adjoining the secondsemiconductor layer section; a third semiconductor layer section on thesecond semiconductor layer section; an insulating layer on the thirdsemiconductor layer section and lower gate structure; a fourthsemiconductor layer section on the insulating layer; a fifthsemiconductor layer section on the fourth semiconductor layer section;and a sixth semiconductor layer section on the fifth semiconductor layersection, wherein the fourth, fifth, and sixth semiconductor layersections are colinear with the first, second, and third semiconductorlayer sections.
 11. The stacked device circuit of claim 10, wherein thefirst semiconductor layer section, second semiconductor layer section,third semiconductor layer section, fourth semiconductor layer section,fifth semiconductor layer section, and sixth semiconductor layer sectionare silicon-germanium (SiGe), and wherein the first semiconductor layersection, third semiconductor layer section, fourth semiconductor layersection, and sixth semiconductor layer section have a lower germaniumconcentration than the second semiconductor layer section and fifthsemiconductor layer section.
 12. The stacked device circuit of claim 11,further comprising an upper gate structure adjoining the fifthsemiconductor layer section and the insulating layer.
 13. The stackeddevice circuit of claim 12, wherein the first semiconductor layersection has a thickness in a range of about 10 nanometers (nm) to about20 nm, the second semiconductor layer section has a thickness in a rangeof about 10 nm to about 30 nm, and the third semiconductor layer sectionhas a thickness in a range of about 10 nm to about 20 nm.
 14. Thestacked device circuit of claim 13, further comprising a contact slabadjoining the sixth semiconductor layer section.
 15. The stacked devicecircuit of claim 14, wherein the fourth semiconductor layer section andsixth semiconductor layer section are doped to form top and bottomsource/drains, and the fifth semiconductor layer section forms a devicechannel of an upper vertical transport field effect transistor segment.16. A stacked device circuit, comprising: a first semiconductor layersection on a substrate; a dielectric fill on the substrate adjoining thefirst semiconductor layer section; a second semiconductor layer sectionon the first semiconductor layer section; a lower gate structure on thedielectric fill and adjoining the second semiconductor layer section; athird semiconductor layer section on the second semiconductor layersection; an insulating layer on the third semiconductor layer sectionand lower gate structure; and a fourth semiconductor layer section onthe insulating layer, wherein the fourth semiconductor layer section isvertically stacked above and colinear with the first semiconductor layersection, second semiconductor layer section, and third semiconductorlayer section.
 17. The stacked device circuit of claim 16, wherein thefirst semiconductor layer section, second semiconductor layer section,and third semiconductor layer section have the same width, W, in a rangeof about 10 nm to about 90 nm.
 18. The stacked device circuit of claim17, further comprising a fifth semiconductor layer section on the fourthsemiconductor layer section; and a sixth semiconductor layer section onthe fifth semiconductor layer section, wherein the fourth, fifth, andsixth semiconductor layer sections are colinear with the first, second,and third semiconductor layer sections.
 19. The stacked device circuitof claim 18, an upper gate structure on the insulating layer andadjoining the fifth semiconductor layer section.
 20. The stacked devicecircuit of claim 19, wherein the lower gate structure is electricallyconnected to the upper gate structure.